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The deepest and most detailed look ever made of the distant cosmos has revealed that black holes were abundant in the early universe, and that they behaved in more varied ways than researchers expected.
At a press conference Tuesday at NASA Headquarters, researchers said they had also spotted the
most distant quasar ever seen -- a discovery that may precede a slew of such findings in coming months and is expected to help illuminate the chemical makeup of the early universe. Combining the power of the orbiting Hubble and Chandra observatories and other ground-based telescopes, two groups of researchers surveyed two patches of sky and combined visible, infrared and X-ray images to provide what they say is proof that black holes of all sizes ruled the early universe.
The research found evidence that as many as 200 million supermassive black holes and even more small, star-sized black holes existed in the early universe, which is thought to be between 12 billion and 15 billion years old.
Scientists have grown to suspect that black holes exist at the centers of most or all galaxies, but it is not known when they developed or whether they have increased or decreased in number or intensity since then. The new study "is the deepest and most comprehensive look we've had at the distribution of black holes and the variety of behavior in them," said Harvey Tananbaum, director of the Chandra X-ray Center.
The two telescopes surveyed a pair of relatively small patches of sky, one in the Northern Hemisphere and one to the south. Chandra's southern view covered an area about the size of the full Moon as it appears from Earth. But each set of observations "goes very deep in that patch," Tananbaum said in a telephone interview. "Presumably what we're seeing in these two patches is typical of the rest of the sky."
The studies found black holes that are up to 12 billion light-years away, which means
the light and X-ray energy researchers studied was emitted 12 billion years ago, when the universe was very young. "The Chandra data show us that giant black holes were much more active in the past than at present," said Riccardo Giacconi, a Johns Hopkins University researcher who led the one of the study.
Giacconi said the patch of sky his group studied found some 350 supermassive black holes -- at a rate of about one per day. Extrapolated to the whole sky, he said this would amount to 200 million of the objects throughout the early universe.
Black holes everywhere
Black holes are massive objects that cannot be seen. Scientists theorize their existence based on the effects they have on their surroundings. The most notable effect is gravity. A black hole's tremendous mass is concentrated in an infinitely small space, and they exert incredible gravity on surrounding matter and energy. Once in the grip of a black hole, nothing can escape, not even light.
Supermassive black holes at the centers of galaxies are often actively gobbling stars and gas in mass quantities. Tremendous energy is created as this matter swirls inward and approaches the speed of light. The colossal friction generates the X-ray emissions that researchers use to identify black holes.
Other black holes, like the one at the center of our Milky Way Galaxy, are relatively quiescent and in some cases do not emit significant amounts of X-rays.
By combining the images, researchers figured out what sorts of galaxies emitted X-rays most intensely, indicating that their black holes were active. "It's often not the biggest and the brightest, the nearest, or the ones with the most stars" that emit the most X-rays, Tananbaum said. "It's sometimes a rather faint, nondescript [galaxy] that may be sitting not too far from much brighter, otherwise more spectacular looking galaxy."
Next page: Revealing more than just black holes
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